Remote reading magnetic compasses are known wherein an electrical signal representation of compass heading is provided and which can be conveyed to one or more remote points for display of compass headings or for other purposes such as in an automatic piloting system. A particularly effective remote reading compass is shown in copending patent application, Ser. No. 279,723 filed Aug. 10, 1972 now U.S. Pat. No. 3,888,016 entitled DIGITAL COMPASS, assigned to the same assignee as this invention. In the compass of this copending application, a compass card is provided in the form of a disc having a plurality of optically coded tracks which are photoelectrically sensed to provide an electrical signal representation of compass headings and which signal is electronically processed to provide a digital pulse train adapted for serial transmission to a remote display or other utilization apparatus.
It is usually desirable in a magnetic compass to provide appropriate damping of the compass card thereby to minimize spurious motion of the card such as caused by rolling, pitching and yawing motions of a vessel aboard which the compass is installed or by other spurious forces, which could give rise to inaccurate compass readings. Such damping is usually accomplished mechanically by immersing the compass structure in a damping liquid having the required viscous properties to minimize spurious card motion. However, such damping necessarily reduces the sensitivity of the compass to changes of heading and it is, of course, desirable to maintain as accurate and sensitive a compass structure as possible while still maintaining sufficient damping to provide a commercially realistic instrument.